DS18b20 and onewire - output problems

Im using Duemlanove with Drobot 1820b sensors with 4k7 resistor and Miles Dallas temperature library. Using his 'simple' sketch the response is -72C which ouputs constantly. using 'single' sketch output is 0C 32F. these outputs are constant regardless of heat applied to the DS18b20, this suggested prob could be sensor, but ive tried 3 now to no avail !! Ive also tried parasitic & powered modes which give same results. Using sheepdog software (no onewire lib) I again got constants which didnt change. any guidance gratefully received

Seems to me a hardware problem.

How do you connect the sensor to the Arduino? which pins etc.

I was playing with those sensors and found that the library could at times set the resolution but not check it was set. Then it would read back rubbish. Depending on the exact code you are using, I would make sure that:

  • After reading from the sensor the CRC is checked
  • After changing resolution read back to make sure it actually changed (including checking the CRC)